1. Field of the Invention
The present invention relates to rubber compositions and methods of making. More particularly, the present invention relates to rubber compositions including solid magnetizable particles bonded to the rubber matrix and methods of making.
2. Description of Background Information
The present invention is especially directed to a further improvement upon the invention described in U.S. Pat. No. 5,913,240 entitled xe2x80x9cMethod and Device for Controlling Slip and/or for Determining the Longitudinal Force or Flex Work-Proportional Parameter, and Vehicle Tire Thereforexe2x80x9d, assigned to Continental AG and incorporated herein by reference. Further, the present invention is preferably combined with the disclosure of DE 196 46 251 of the same assignee. U.S. Pat. No. 5,895,854, which is also incorporated herein by reference, claims priority of this German application.
Beside the patents mentioned above and incorporated herein, we became aware of German patent applications DE 195 03 468 C1 and DE 195 03 469 C1, both being published May 30, 1996 and citing U.S. Pat. Nos. 4,161,120; 4,948,277; 5,017,868; 5,026,178; 5,131,763; 5,261,752; and 5,261,753.
Further, we became aware of European patent applications EP 0 890 752 A2 and EP 0 890 753 A2, both published Jan. 13, 1999; and EP 0 892 185 A2, published Jan. 20, 1999.
It is an object of this invention to detente or defuse the present conflict in measuring out the best dose of solid magnetizable particles to be imbedded in a polymer matrix or network, this conflict being recognized by us, the inventors, between:
a first goal of attaining high fatigue life and high crack growth resistance, both demanding a low or null dose of solid magnetizable particles, and
a second goal of attaining a strong magnetic signal by passing discrete magnetized areas of a circumferential row of magnetized areas along a sensor, demanding a high dose of solid magnetizable particles.
In an environmentxe2x80x94such as a vehiclexe2x80x94there exist many low magnetic influences. In view of the relatively great distance (ca. half an inch for passenger cars) between magnetized areas of a tire and a sensor, it is a further object of the invention to generate the intended sequence of signals by strong magnetic areas, avoiding misrecognition of the passing times of magnetic areas and thus avoiding mismeasurements of forces acting on a tire and missignals given to brake controllers or brake actuators.
We, the inventors, have recognized that in those rubber compositions known in the art, the solid magnetizable particles function as flaw sites to initiate cracking and component failure when subjected to repeated deformation. Evidence of this is provided in FIGS. 1 and 2, showing fatigue life and crack growth resistance of a standard black tire sidewall composition versus a composition A containing 200 phr of a ferrite filler.
The primary reason for this unintended effect is the great difference between the stiffness of the matrix and that of the solid magnetizable particles; unfortunately this primary reason is unavoidable. But with a stronger bonding between the matrix and the solid magnetizable particles, the loss of fatigue resistance and crack growth resistance will be reduced. Therefore we focussed our labor on enhancing bonding between solid magnetizable particles and surrounding molecules of the rubbery compounds.
As a solution, we provide a chemical coupling agent and also a special mixing technique to provide a chemical bond between the magnetized particles and the polymer matrix, thereby allowing additional mechanisms for fatigue and tearing energy dissipation. Such chemical coupling agents can be, but are not limited to, organo-functional silane materials. This invention allows the filling of a rubber composition with a high level of solid magnetizable particles, also described as xe2x80x9cmagnetic fillersxe2x80x9d, without diminishing too much fatigue resistance and crack growth resistance. Thus, magnetic fillers can be incorporated successfully in rubber compositions which are used for high flex components, especially for tire sidewalls.
Advantageously, our invention is facilitated by the fact that such organo-functional silane materials may be used which are already well-known in the rubber industry. However, up-to-date organo-functional silane materials are used only in rubber compositions for tire treads and not in compositions for tire sidewalls. In these tread rubber compositions, organo-functional silane materials are combined with silica and provide bonding of the silica to the polymer matrix; they are not combined with any solid magnetizable particle and therefore do not provide or disclose any bonding of such particles to the polymer matrix.
Beside the solid magnetizable particles, the rubber composition of the present invention contains molecules of natural and/or artificial polymer and/or other fillers such as carbon black, silica and/or other compounds such as sulfur, as a chain-building ingredient, vulcanizing accelerators, vulcanizing retarders and so on. These surrounding molecules are a matrix in which the solid magnetizable particles are imbedded.
Differences between this invention and other known arrangements include the use of chemical coupling agents to bond magnetic powder to the polymer matrix, and the special mixing technique to maximize reaction between coupling agent, magnetic powder, and polymer matrix.